The present invention relates generally to heat-transfer labels and more particularly to heat-transfer labels that include a non-wax release layer or a non-wax release coating.
Heat-transfer labels are commonly used in the decorating and/or labelling of commercial articles, such as, and without limitation to, containers for beverages (including alcoholic beverages, such as beer), essential oils, detergents, adverse chemicals, as well as health and beauty aids. As can readily be appreciated, heat-transfer labels are desirably resistant to abrasion and chemical effects in order to avoid a loss of label information and desirably possess good adhesion to the articles to which they are affixed.
One of the earliest types of heat-transfer label is described in U.S. Pat. No. 3,616,015, inventor Kingston, which issued October, 1971, and which is incorporated herein by reference. In the aforementioned patent, there is disclosed a heat-transfer label comprising a paper sheet or web, a wax release layer affixed to the paper sheet, and an ink design layer printed on the wax release layer. In the heat-transfer labelling process, the label-carrying web is subjected to heat, and the label is pressed onto an article with the ink design layer making direct contact with the article. As the paper sheet is subjected to heat, the wax layer begins to melt. This enables the paper sheet to be released from the ink design layer, with a portion of the wax layer being transferred with the ink design layer onto the article and with a portion of the wax layer remaining with the paper sheet. After transfer of the design to the article, the paper sheet is immediately removed, leaving the design firmly affixed to the article and the wax transferred therewith exposed to the environment. The wax layer is thus intended to serve two purposes: (1) to provide release of the ink design from the web upon application of heat to the web and (2) to form a protective layer over the transferred ink design. After transfer of the label to the article, the transferred wax release layer is typically subjected to a post-flaming technique which enhances the optical clarity of the wax protective layer (thereby enabling the ink design layer therebeneath to be better observed) and which enhances the protective properties of the transferred wax release.
Many heat-transfer labels include, in addition to the layers described above, an adhesive layer (comprising, for example, a polyamide or polyester adhesive) deposited over the ink design to facilitate adhesion of the label onto a receiving article. An example of a heat-transfer label having an adhesive layer is disclosed in U.S. Pat. No. 4,548,857, inventor Galante, which issued Oct. 22, 1985, and which is incorporated herein by reference. Additionally, many heat-transfer labels additionally include a protective lacquer layer interposed between the wax release layer and the ink layer. An example of such a label is disclosed in U.S. Pat. No. 4,426,422, inventor Daniels, which issued Jan. 17, 1984, and which is incorporated herein by reference.
One phenomenon that has been noted with heat-transfer labels of the type described above containing a wax release layer is that, quite often, a degree of hazing or a “halo” is noticeable over the transferred label when the transfer is made onto clear materials. This “halo” effect, which persists despite post-flaming and which may detract from the appearance of the label, is caused by the presence of the wax coating around the outer borders of the transferred ink design layer. Hazing due to the wax release layer may also appear in “open-copy” areas of the label, i.e., areas of the label where no ink is present between the adhesive and protective lacquer layers, and also may detract from the appearance of the label.
In addition to and related to the aforementioned problem of hazing, when heat-transfer labels of the type described above are applied to dark-colored containers, the outer wax layer of the label often appears as a whitish coating on the container, which effect is undesirable in many instances. Furthermore, scratches and similar abrasions to the outer wax layer of the label can occur easily and are readily detectable.
Accordingly, to address the aforementioned issues, considerable effort has been expended in replacing or obviating the need for a wax release layer. One such approach to this problem is disclosed in U.S. Pat. No. 3,922,435, inventor Asnes, which issued Nov. 25, 1975, and which is incorporated herein by reference. In the aforementioned Asnes patent, which relates to a heat-transfer label for objects such as plastic bottles, the customary release layer of wax is replaced with a release layer of a non-wax resin. This non-wax resinous layer is referred to in the Asnes patent as a dry release since it does not transfer to the article along with the ink design layer and is said to comprise a thermoset polymeric resin, such as cross-linked resins selected from the group consisting of acrylic resins, polyamide resins, polyester resins, vinyl resins, epoxy resins, epoxy-acrylate resins, allyl resins, aldehyde resins, such as phenol-formaldehyde resins and the amino-aldehyde resins, e.g., urea formaldehyde or melamine formaldehyde, and combinations thereof.
The heat-transfer label of the foregoing Asnes patent also comprises a clear lacquer layer which is printed onto the release layer, a design print (which may include a number of ink layers) which is printed onto the clear lacquer layer, and a heat-activatable adhesive layer which is printed onto the design print and the clear lacquer layer. The Asnes patent explicitly teaches that “the design print and the adhesive print are both located marginally wholly within the lacquer print. The adhesive layer may be of the same area or larger in area than the design print so long as it is smaller in area than the lacquer print.” The Asnes patent also teaches that “it is highly preferred that neither the release layer nor the lacquer layer, at least where they are in contact with each other, contain any substance which is oily or liquid at heat transfer temperature since the oil or liquid, like the wax in wax release layers, will part, leaving some on the lacquer surface and some on the removed release surface.”
Another example of a heat-transfer label comprising a non-wax release layer is disclosed in U.S. Pat. No. 4,935,300, inventors Parker et al., which issued Jun. 19, 1990, and which is incorporated herein by reference. In the aforementioned Parker patent, the label, which is said to be particularly well-suited for use on high density polyethylene, polypropylene, polystyrene, polyvinylchloride and polyethylene terephthalate surfaces or containers, comprises a paper carrier web which is overcoated with a layer of thermoplastic polyethylene. A protective lacquer layer comprising a polyester resin and a relatively small amount of a nondrying oil is printed onto the polyethylene layer. An ink design layer comprising a resinous binder base selected from the group consisting of polyvinylchloride, acrylics, polyamides and nitrocellulose is then printed onto the protective lacquer layer. A heat-activatable adhesive layer comprising a thermoplastic polyamide adhesive is then printed onto the ink design layer.
Although the above-described Parker label substantially reduces the wax-related effects discussed previously, said label does not quite possess the same release characteristics of heat-transfer labels containing a wax release layer. In fact, when put to commercial use, the polyethylene release layer of the Parker label was found to become adhesive when subjected to the types of elevated temperatures typically encountered during label transfer. Accordingly, another type of heat-transfer label differs from the Parker heat-transfer label in that a very thin layer or “skim coat” of carnauba wax is interposed between the polyethylene release layer and the protective lacquer layer to improve the release of the protective lacquer from the polyethylene-coated carrier web. The thickness of the skim coat corresponds to approximately 0.1-0.4 lbs. of the wax spread onto about 3000 square feet of the polyethylene release layer. The aforementioned “skim coat-containing” heat-transfer label also differs from the Parker label in that the heat-activatable adhesive of the “skim coat” label is printed over the entirety of the ink and protective lacquer layers, with the peripheral edges of the adhesive layer in direct contact with the wax skim coat.
An example of a “skim coat-containing” heat-transfer label of the type described above is disclosed in U.S. Pat. No. 5,800,656, inventors Geurtsen et al., which issued Sep. 1, 1998, and which is incorporated herein by reference. According to one embodiment, the Geurtsen label is designed for use on silane-treated glass containers of the type that are subjected to pasteurization conditions, the label including a support portion, a skim coat positioned on top of the support portion and a transfer portion positioned on top of the support portion. The support portion includes a sheet of paper overcoated with a release layer of polyethylene. The transfer portion includes an organic solvent-soluble phenoxy resin protective lacquer layer, an organic solvent-soluble polyester resin ink layer over the protective lacquer layer, and a water-dispersible acrylic adhesive resin layer over the ink and protective lacquer layers and onto a surrounding portion of the skim coat.
Although the release properties of heat-transfer labels that include the aforementioned wax skim coat are much improved compared to similar heat-transfer labels lacking said wax skim coat, said labels do result in a portion of the wax skim coat being transferred to the article being decorated during label transfer. As a result, particularly when the labelled article is dark in color, a wax residue is often visible to the naked eye on the article around the peripheries of the label and in open-copy areas of the label. Such a wax residue, for the reasons discussed above, is undesirable from an aesthetic standpoint. In addition, said wax residue precludes the possibility of decorating articles, such as containers, with “wrap-around” labels of the type that completely encircle an object since the adhesive present at the trailing end of the label will not adhere to that portion of the article covered by the wax residue that is deposited with the leading end of the label.
Heat-transfer labels of the type that include the aforementioned wax skim coat are typically heated during the labelling process in order to cause the wax skim coat to soften, thereby facilitating label transfer. However, the heating temperatures needed to soften the wax skim coat have become increasingly more difficult to achieve as new decorating systems are being developed in which bottle throughput is higher and, consequently, the dwell time for heating is shorter, and the actual heating temperatures are lower.
Yet another example of a heat-transfer label comprising a non-wax release layer is disclosed in PCT Appln. No. PCT/US89/01731, inventors Abber et al., which was published Feb. 8, 1990, and which is incorporated herein by reference. In the aforementioned Abber PCT application, a heat-transfer label for application to a plastic bottle or container is described that includes a carrier sheet and a transferable substrate affixed to the carrier sheet. The carrier sheet includes a nonwax thermoset release layer coated over a paper sheet. The nonwax thermoset release layer is a noncellulosic alkyd resin formed by the crosslinking of an alkyd polymer with a methoxy melamine to produce a thermoset release. The alkyd polymer employed is preferably of the type formed by the thermosetting reaction product of a hydroxy-functional polyester with a drying oil. The transferable substrate affixed to the carrier sheet includes a nonwax lacquer transfer layer, an ink design layer over the lacquer transfer layer and a heat-activatable adhesive layer over the ink design layer.
Still another example of a heat-transfer label comprising a non-wax release layer is disclosed in PCT Appln. No. PCT/EP97/00642, inventors Ast, which was published on Aug. 14, 1997, and which is incorporated herein by reference. In the aforementioned Ast PCT application, the release layer is made of polypropylene or polyethylene.
Still yet another example of a heat-transfer label comprising a non-wax release layer is disclosed in European Patent Appln. No. 824,251, inventors Brandt et al., which was published on Feb. 18, 1998, and which is incorporated herein by reference. In the aforementioned Brandt EPO application, there is disclosed a heat-transfer label that is designed for use on a crate and that, once applied to a crate, can easily be removed therefrom in a washing process without the ink dissolving in the wash liquid. The foregoing Brandt label comprises a backing layer and a transfer layer, the transfer layer being releasably attached to the backing layer. The backing layer comprises a polypropylene film coated with a silicone layer. The transfer layer comprises a first containment layer in contact with the silicone layer, an ink layer on top of the first containment layer and marginally wholly within the first containment layer, a second containment layer on top of the ink layer and on top of the first containment layer, the first and second containment layers contacting one another outside the perimeter of the ink layer to form a closed envelope around the ink layer, and an adhesive layer on top of the first and second containment layers, the first containment layer and the adhesive layer contacting one another outside the perimeter of the second containment layer to form a closed envelope around the ink layer and second containment layer.
Unfortunately, the use of silicone as a release coating, as in the preceding example, presents certain problems or shortcomings. One of these problems is the difficulty of printing a label on a silicone release. Other possible problems or shortcomings are set forth in U.S. Pat. No. 5,314,929, inventors Crivello et., which issued May 24, 1994, and which is incorporated herein by reference. In the aforementioned Crivello patent, there is disclosed a silicone-free release coating composition adapted for use with adhesive tapes, said silicone-free coating composition being said to be rapidly curable and comprising (a) between about 50 and about 95 wt % of an alkyl vinyl ether monomer having the formula CnH2n+1O—CH—CH2 wherein n has a value of from 8 to 20, optionally containing a cationically polymerizable comonomer; (b) between about 5 and about 50 wt % of a multifunctional vinyl ether monomer and (c) between about 0.1 and about 10 wt % of an onium salt photoinitiator.
It is to be noted that the aforementioned Crivello patent neither teaches nor suggests the use of its release composition as a release coating in a heat-transfer label.